In general, power transfer mechanisms, such as transfer cases, may be operatively associated with either manual or automatic transmissions for selectively directing power from an engine to a first set of driven wheels in a two-wheel drive mode as well as selectively directing power to the non-driven wheels for operation in a four-wheel drive mode. Many transfer cases provide for a mode shift when transferring between two wheel and four wheel drive modes as well as a range shift to provide at least two different reduction ratios to the driven wheels.
Some transfer cases include a range shift system for axially translating a range sleeve between low range, neutral and high range positions. The range shift system also includes a range shift fork for the application of force to the range sleeve. The range shift fork is trapped between compression springs within a range bracket. To achieve a range shift, an actuator applies a force to the range bracket. The range bracket is translated causing a transfer of force through one of the springs to the range fork. If the teeth of the range sleeve and the driven components are aligned, axial translation of the range fork, the springs and the range bracket occurs. If the shift is blocked due to misalignment of the range sleeve teeth and the teeth of the associated driven component, the range bracket will continue to be translated to its desired position but the range fork will not translate and the spring will compress. Once the range clutch teeth align, the spring will drive the range fork and the range sleeve to the desired position.
On some occasions, the range shift system previously described suffers from certain deficiencies due to the high magnitude of torque transferred by the transfer case. In some instances, a main shaft containing the drive gears incurs a bending moment sufficient to affect the interface between the range gear set and the range sleeve teeth causing misalignment therebetween. The misalignment may place an axial load on a range sleeve pushing it against the range spring out of the drive gear and into neutral. While one remedy for this concern may be to increase the stiffness of the range spring to withstand the axial forces on the range sleeve and maintain the desired drive arrangement, the higher rate spring introduces other concerns. Specifically, the high rate spring resists compression by the range shift actuator such that the spring does not compress if a blocked shift occurs. In these instances, when a block occurs, the system will not successfully shift. The operator may be required to move the vehicle and attempt the range shift again.
Accordingly, it may be desirable to provide an improved range shift system that reduces the tendency to inadvertently shift into neutral while also allowing a range shift that does not require additional drive or input when a blocking condition exists.